Introduced in 1961, it served in the United States Navy as a key ASW and utility asset for several decades before being replaced by the non-amphibious Sikorsky SH-60 Seahawk in the 1990s. The type also proved popular in civil service and with foreign military customers. As of 2015, many remain in service in nations around the world. The Sea King has been built under license by Agusta in Italy, Mitsubishi in Japan, and by Westland in the United Kingdom as the Westland Sea King. The major civil versions are the S-61L and S-61N.

During the Cold War, the Soviet Navy built a submarine fleet that at one point included more than 200 operational submarines. The US Navy countered by developing various anti-submarine warfare (ASW) capabilities, including the Sea King.[3]

In 1957, Sikorsky was awarded a contract to produce an all-weather amphibious helicopter for the U.S. Navy. The new helicopter was to excel at ASW and would combine the roles of hunter and killer; these duties had previously been carried out by two separate helicopters.[4] Key features of the emerging ASW helicopter would include its amphibioushull for landing on water, and its twin-turboshaft engines that enabled a larger, heavier and better-equipped aircraft than prior helicopters.[4][5]

The first prototype took flight for the first time in March 1959.[4] Carrier suitability trials were conducted on board Lake Champlain; the trials were completed successfully in mid-1961.[6] The US Navy began receiving delivery of the first HSS-2 aircraft, which would be subsequently re-designated as the SH-3A, in September 1961.[7]

In late 1961 and early 1962, a modified U.S. Navy HSS-2 Sea King was used to break the FAI 3 km, 100 km, 500 km and 1000 km helicopter speed records. This series of flights culminated on 5 February 1962 with the HSS-2 setting an absolute helicopter speed record of 210.6 mph.[11] This record was broken by a modified French Sud-AviationSuper Frelon helicopter on 23 July 1963 with a speed of 217.7 mph.[12]

In US Navy service, the initial SH-3A model of the Sea King would be progressively converted into the improved SH-3D and SH-3H variants; these featured more powerful engines and improved sensors that gave the type greater operational capabilities as an ASW platform. It was also common for Sea Kings to be converted for non-ASW activities, these roles included minesweeping, combat search and rescue, and as a cargo/passenger utility transport.[4] The aircrew on ASW-tasked Sea Kings were routinely trained to carry out these secondary roles as aircraft could often be quickly adapted to perform different missions in the face of operational needs.[13]

The Royal Canadian Navy (RCN) became a major operator of the type (see Sikorsky CH-124 Sea King), the Sea King continues to operate as Canada's dominant maritime helicopter 50 years following its introduction to service in 1963.[14] One notably innovation in Canadian operations, which was subsequently adopted by several other nations, was the use of a winch 'hauldown' landing method, referred to as a 'Beartrap'. This device considerably increased the ability of Sea Kings to land in difficult conditions, such as on small flight decks or during poor weather conditions.[14][15]

In the early 21st century, following their drawdown in US service, there have been a number of initiatives to refurbish ex-military Sea Kings for continued operations; in addition to civil operators, nations such as Egypt and India acquired refurbished former US Sea Kings to supplement their own ageing fleets.[21][22][23] While Sikorsky had ended production of the type during the 1970s, it was reported that nearly 600 Sea Kings were in operational service in 2009.[24]

The Sea King was a considerable advancement over previous helicopters. Its twin-turboshaft powerplant layout gave the SH-3 far better payload and reliability than previous anti-submarine helicopters.[4] If one engine fails, the Sea King can keep flying on a single engine.[25] Sea Kings typically had a four-man crew. A pilot and copilot in the cockpit and two aircrew in the cabin area. On anti-submarine missions, the rear aircrew operated and monitored the aircraft's detection equipment and interpreted the sensor data.[26] For search-and-rescue missions, the cabin can accommodate up to 22 survivors or nine stretchers plus two medical officers. For troop transport, up to 28 soldiers can be accommodated.[citation needed]

The Sea King features many design elements to support naval-orientated operations; the main rotor blades and the tail section can be folded for storage on ships. An amphibioushull allows most Sea Kings to land on and remain on the ocean's surface; deployable airbags in the aircraft's sponsons add stability and buoyancy.[5]

The armament fitted upon a Sea King could vary considerably. For anti-submarine missions, the aircraft could carry up to four torpedoes or four depth charges. For anti-ship duties, some models were outfitted to carry one or two missiles, typically Sea Eagles or Exocets.[27] The Sea King could also be fitted to deploy the B57 nuclear bomb.[28]

ASW equipment used on Sea Kings has included the AQS-13A/B/E dipping sonar, specialized computers for processing sonar and sonobuoy data, various models of sonobuoys, ARR-75 Sonobuoy Receivers, and Magnetic Anomaly Detectors. The commonly fitted AKT-22 data link enabled the rapid dissemination of gathered sonar information to other friendly elements in range.[29] Some later Sea King models featured digital navigation systems and overhauled cockpit instrumentation for night vision compatibility.[30]

The Sea King became operational with the United States Navy in June 1961 as the HSS-2. When the unified aircraft designation system was introduced, the aircraft's designation changed to SH-3A. It was used primarily for anti-submarine warfare: detecting and tracking Soviet submarines. In time of war, it would have attacked them as well.[31] Sea Kings could also operate from offshore platforms to extend their surveillance and strike range. Nighttime ASW operations were possible with considerable difficulty.[32][33]

The Sea King also performed various other roles and missions such as search-and-rescue, transport, anti-shipping and airborne early warning operations. Aircraft carriers would typically deploy Sea Kings to operate near the carrier as a plane guard, ready to rescue air crew who crashed during takeoff or landing.[34] They routinely transferred personnel and mail between vessels.[32]

During the Vietnam War, SH-3s rescued the crews of downed aircraft at sea and over land, using self-sealing fuel tanks, machine guns and armor.[38] The Sea King was also used for medical evacuations and disaster relief efforts.[32]

Several Sea Kings, operated by the United States Marine Corps's HMX-1 unit, are used as the official helicopters of the President of the United States; in this capacity, the call sign 'Marine One' is used by the helicopter currently occupied by the President. As of 2012, a replacement helicopter fleet for the Sea King is pending under the VXX program.[41][42] In 1992, the US Justice Department sued Sikorsky over allegations of overcharged component pricing and deliberately misleading US Navy negotiators.[43] In 1997, the Justice Department issued further accusations against Sikorsky of willful overcharging on a contract to upgrade the Navy's Sea Kings.[44]

During the 1990s, the Sea King was replaced in the ASW and SAR roles by the U.S. Navy with the newer Sikorsky SH-60 Sea Hawk.[45] However, the SH-3 continued to operate in reserve units in roles including logistical support, search and rescue, and transport. On 27 January 2006, the SH-3 was ceremonially retired at NAS Norfolk, Virginia, by Helicopter Combat Support Squadron 2 (HC-2).[46] They have been replaced by increasingly advanced variants of the SH-60 Sea Hawk.[32]

Combat search and rescue helicopter for the U.S. Navy. 12 converted from SH-3A.[4]

CH-3A

Military transport version for the U.S. Air Force; three converted from SH-3As into CH-3A configuration; they later became CH-3Bs.[49]

NH-3A (S-61F)

Experimental high-speed compound helicopter, with extensive streamlining, no floats, short wings carrying two turbojet engines for extra speed; one converted from SH-3A.[citation needed] Later modified with a tail rotor able to rotate 90° to serve as a pusher propeller; this helicopter demonstrated "Roto-Prop" pusher propeller for Sikorsky's S-66 design.[50]

RH-3A

Minesweeper helicopter for the U.S. Navy. Nine converted from SH-3A aircraft.[47]

VH-3A

VIP transport helicopter for the U.S. Army and Marine Corps; originally designated HSS-2Z. Eight built, plus two SH-3A conversions rebuilt from damaged helicopters (one YHSS-2 and one SH-3A).[citation needed] The rest were returned to the U.S. Navy in 1975–76 and replaced by the VH-3D.

VIP transport helicopter for the U.S. Marine Corps. It entered service in 1976.[51]

SH-3G

Cargo, utility transport helicopter for the U.S. Navy. 105 conversions from SH-3A and SH-3D.[4]

SH-3H (HSS-2B)

Upgrade of the SH-3G as an anti-submarine warfare (ASW) helicopter for the U.S. Navy.[4] It included SH-3G features with improvements for ASW, anti-ship missile detection and other airframe improvements. 163 SH-3Gs were upgraded to SH-3H configuration.[51]

SH-3H AEW

Airborne early warning version for the Spanish navy.

UH-3H

Cargo, utility transport version for the U.S. Navy; converted from SH-3H by removing ASW systems.[51]

The Sea King Improvement Program (SKIP) added modernized avionics as well as improved safety features.[54]

CH-124B

Alternate version of the CH-124A without a dipping sonar but formerly with a MAD sensor and additional storage for deployable stores. In 2006, the five aircraft of this variant were converted to support the Standing Contingency Task Force (SCTF), and were modified with additional troop seats, and frequency agile radios. Plans to add fast-rope capability, EAPSNIPS (Engine Air Particle Separator / Snow & Ice Particle Separator) did not come to fruition.[54]

CH-124B2

Six CH-124B's were upgraded to the CH-124B2 standard in 1991–1992. The revised CH-124B2 retained the sonobuoy processing gear to passively detect submarines but was also fitted with a towed-array sonar to supplement the ship's sonar. Since anti-submarine warfare is no longer a major priority within the Canadian Forces, the CH-124B2 were refitted again to become improvised troop carriers for the newly formed Standing Contingency Task Force.[54]

CH-124C

One CH-124 operated by the Helicopter Operational Test and Evaluation Facility located at CFB Shearwater. Used for testing new gear, and when not testing new gear, it is deployable to any Canadian Forces ship requiring a helicopter.[54]

CH-124U

Unofficial designation for four CH-124s that were modified for passenger/freight transport. One crashed in 1973, and the survivors were later refitted to become CH-124A's.[54]